# 3D convolution output shape

Hello,

I have the following 3D CNN that I use to predict the value (a property we want to predict) from the 3D images.

I want to compute the loss as Mean Absolute error (L1 loss) of each batch.

My current settings are:
(batch size=1)
image size = (64,64,64)
the input tensor of images from train_loader to the network is shape of =[1,1,64,64,64]
[1 for batch size of 1, 1 greyscale input (1 channel), 64 z dim, 64 x dim, 64 y dim]

class CNN3D(nn.Module):
def init(self):
super(CNN3D,self).init()
self.bn1=nn.BatchNorm3d(32)
self.pool1=nn.AvgPool3d(2,stride=2)
self.bn2=nn.BatchNorm3d(64)
self.fc1=nn.Linear(7764,500)
self.fc2=nn.Linear(500,50)
self.fc3=nn.Linear(50,1)

``````def forward(self,x):
x=self.pool1(F.relu(self.bn1(self.conv1(x))))
x=self.pool2(F.relu(self.bn2(self.conv2(x))))
x=x.view(-1,7*7*64)
x=F.relu(self.fc1(x))
x=F.relu(self.fc2(x))
x=self.fc3(x)

return x
``````

The output of the network (predictions) is shape: torch.Size([56, 1])
The actual labels size are: torch.Size([1])

Shouldn’t be the size of the network output be a torch.Size([1)]? I don’t get why it outputs torch.Size([56, 1])?

My question is how do i fix the output of the network to be a something like (N,1) where N is the batch size. Because the size of the network predictions and the actual labels should have the same size!

Can somone help?

Can you print the shape of x after each line in forward and show the results ?

@Balamurali_M & @Naif40
There is a great reference for understanding different kinds of Convolution Operators (3D Convolution, Spatially separable convolution, depthwise separable convolution, etc.):